*With air flow. Maxim Integrated Products 1

Transcription

1 9-94; Rev ; 3/0 MX003-0W Evaluation Kit General Description The MX003 0W forward converter evaluation kit (EV kit) provides a regulated +V output voltage at currents up to 0, when operated from a +3V to +7V input voltage range. This EV kit is fully assembled and tested. The output voltage is preset to +V. single-transistor forwardconverter topology with a reset winding is used for high output power and high efficiency. The use of an optocoupler in the feedback circuit provides full 00V primary to secondary galvanic isolation. bottom-mounted heatsink plate safely dissipates the heat generated by the power MOSFET and the output diode. The power supply is designed to fit into a small footprint. WRNING: Dangerous voltages are present on this EV kit and on equipment connected to it. Users who power-up this EV kit or power the sources connected to it must be careful to follow safety procedures appropriate to working with high-voltage electrical equipment. Under severe fault or failure conditions, this EV kit may dissipate large amounts of power, which could result in the mechanical ejection of a component or of component debris at high velocity. Operate this EV kit with care to avoid possible personal injury. DESIGNTOR QTY DESCRIPTION C, C 3, C 0, C 4 ceramic caps (080) C 470pF ceramic cap (080) C4, C, C µF, ceramic caps (0) C7, C3, C4 3 0µF,.3V electrolytic capacitors Nichicon UPW0JMPH C8, C9 47nF ceramic capacitors (080) C nf ceramic capacitor (080) C nf, ceramic capacitor (080) C 4.7nF, 00V ceramic capacitor D3 D4 D 00m, diode Panasonic MCT 0, 40V low forward voltage Schottky diode General Semi SBL040CT 00m, 00V, diode Panasonic MCT Q 00V MOSFET, Rds = 0.8Ω International Rectifier IRF40N Q NPN transistor, FMMT3904 Features +V at 0 Output ±3V to ±7V Input Voltage Range 0kHz Switching Frequency Fully Isolated Design with 00V Isolation Built into the Transformer Fully ssembled and Tested Board with Minimum PC Board Footprint 0.3% typical Line and Load Regulation 8% typical Efficiency at W Ordering Information PRT TEMP RNGE IC PCKGE MX003EVKIT0W 0 C to +0 C* SO *With air flow. Component List DESIGNTOR QTY DESCRIPTION R MΩ ± resistor (080) R 39.kΩ ± resistor (080) R3 80.kΩ ± resistor (080) R4.4kΩ ± resistor (080) R kω ± resistor (080) R 0.0Ω resistor Dale-Vishay WSL0 0.0Ω ±.0% R8 R8 00Ω ±% resistor (080) R9 470Ω ±% resistor (080) R, R 0kΩ ± resistors (080) R3 0Ω ±% resistor (0) R4 0kΩ ±% resistor (080) R 40kΩ ±% resistor (080) R Ω ±% resistor (080) L T 4.7µH inductor Coiltronics HC-4R7 Transformer (-pin gull wing) Coiltronics CTX03-48 Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at , or visit Maxim s website at

2 MX003-0W Evaluation Kit Component List (continued) DESIGNTOR QTY DESCRIPTION U Optocoupler QT Optoelectronics MOC7 U3 Shunt regulator TL43ID U MX003ESE, -pin narrow SO Z V Zener diode Panasonic M80 Component Suppliers SUPPLIER PHONE FX Coiltronics Dale-Vishay General Semiconductor International Rectifier Nichicon Panasonic QT Optoelectronics Quick Start The MX003 0W EV kit is fully assembled and tested. The power supply has full isolation between the primary and secondary circuit. heatsink is included at the noncomponent side for heatsinking the power MOSFET and the output dual diode D4. During normal operation at full output current, this heatsink becomes hot. small fan with direct airflow towards this heatsink is recommended to keep the temperature rise to acceptable levels. This power supply is not fused at the input. For added protection, a 3 to fuse should be used at the input. ppropriately sized heavy-gauge wires should be used to connect the power supply to the EV kit and load. Follow these steps to verify board operation. Do not turn on the power supply until all connections are made. ) Connect a 0µF bulk storage capacitor at the input terminals of the EV kit. This capacitor should be rated for and be able to handle. of ripple current. ) Connect a +3V to +7V power supply to the pads labeled VIN. The positive power-supply terminal should connect to +V IN and the negative powersupply terminal should connect to -V IN. The power supply must be rated to at least 3. The input voltage to the MX003 EV kit should not exceed 80V at any time. 3) Connect a variable load capable of sinking at least 0 at V and a voltmeter to the pads labeled +V O and -V O. 4) Set the load current to approximately. ) Turn on the input power and verify that the output voltage is +V. ) To evaluate the load regulation of the EV kit, vary the load from 0 to 0 and record the output voltage variation as needed. For best measurement accuracy, the voltmeter must be connected right to the output pads of the EV kit. 7) To evaluate the line regulation of the EV kit, vary the input voltage from +3V to +7V and record the output voltage. Note: The MX003 EV kit undervoltage lockout circuitry has been designed to shut down when the input supply voltage is under 3V. Power Supply Typical Specifications Table summarizes the typical performance of the 0W power supply. Table. Typical Specifications Output Power 0W Input Voltage (V IN ) ±3V to ±7V Output Voltage (V OUT ) +V Output Current (I OUT ) 0 Initial Output ccuracy ±3%* Output Voltage Regulation 0.3%, over line and load Efficiency 8% at 48V and W Input Output Isolation 00V for s Feedforward Compensated Switching Topology Forward Converter Dimensions 4.0in x.3in *Initial setpoint accuracy can be improved by using tighter tolerance resistor divider (R and R).

3 MX003-0W Evaluation Kit EFFICIENCY (%) OUTPUT POWER (W) Figure. Efficiency vs. Output Power VOUT (V) I OUT () MX003EV fig0 MX003EV fig0 VOLTS µs/div Figure 3. Output Transient Response (I OUT : 0 to 0.8) VOUT (V) V/div ms/div MX003 fig04 MX003EV fig03 Figure. Output Voltage Regulation vs. Output Current Power-Supply Performance Key performance characteristics of the power supply include efficiency and output voltage regulation. Figure shows the efficiency vs. output power. The efficiency reaches 8% at about W of output power and stays relatively flat up to 0W. Even though the efficiency is very high, heatsinking is required for the power MOSFET and output diode. The diode will dissipate about W with a 0 output current and the MOSFET can be expected to dissipate about 3W to 4W at full 0W load. Sufficient airflow over the power supply is recommended to cool down the power transformer and output inductor. Figure shows the output voltage regulation of the power supply from 0 to 0 of output current. Voltage measurement was done across the output voltage sense points +V O and -V O. Figure 4. Output Voltage Transient t Power-Up (V IN = 48V, I OUT = ) nother interesting performance waveform for power supplies is the output voltage transient response to a step change in output current. Figure 3 shows load transient response when the load is stepped from 0 to 0.8. s can be seen from Figure 3, the initial transient response time is less than 30µs. This is a side benefit of using an optocoupler in conjunction with a TL43 shunt regulator for isolation. Figure 4 shows the well-behaved startup characteristics of this power supply, which are characterized by the monotonic rise of the output voltage as well as the absence of any overshoots at the end of the rise period. 3

4 MX003-0W Evaluation Kit VDS(V) 0V/div 400ns/div Figure. Drain-Source Voltage Waveform MX003 fig0 The Power Circuit Topology mong the several power topologies available, the single-transistor forward topology offers a simple and lowcost solution and provides very good efficiency throughout the operating power range. However, this topology requires a transformer reset winding connected to pins T 3 and T 4 (Figure 7). The forward converter was chosen because it offers higher power density and higher efficiency than a flyback converter at these power levels. Transformer T provides 00V isolation between primary and secondary. Efficiency is further improved by powering the control circuit from a primary bias winding (T, T, Figure 7) after initial startup. 0kHz switching frequency was selected to allow small form-factor transformer, inductor, and output capacitors. Key Operating Waveforms Key operating waveforms are always useful in understanding the operation of switching power supplies. 0 oscilloscope probe is necessary for effective probing. digital scope is very useful in capturing startup sequences. However, extreme caution should be exercised when probing live power supplies. For example, shorting the drain-source terminals of Q while power is applied is sure to produce a big spark and may damage the EV kit. Figure shows the drain-to-source waveform of Q. Notice the leading-edge voltage spike. This is a result of the energy stored in transformer T s leakage inductance. Figure shows the voltage at the output of the secondary rectifier (cathode of D4). V/div 00ns/div Figure. Waveform at Cathode of D4 MX003 fig0 PC Board Layout and Component Placement s with any other switching power supply, component placement is very important. Because of the primary-tosecondary isolation, the primary and secondary grounds are separated. Figure 0 clearly shows the separation on both sides of the PC board. The layout of the board can be changed to accommodate different footprints. lso, the power MOSFET and output rectifier should be mounted on a heatsink for best thermal management. In this implementation, both of these components are on the noncomponent side of the board, with their tabs mounted to the heatsink plate. The critical layout considerations are as follows: Distance from the secondary transformer leads to diode D4 should be kept to a minimum. This will improve EMI as well as the effective available power transfer. Bypass capacitors C4, C, and C should be as close as possible to T. The PC board trace connecting T to the drain of Q should be as short as possible. The current-sense resistor R should be as close as possible to the source of Q and should return with a very short trace either to the ground plane or to the negative lead of bypass capacitors C4, C, and C. The gate-drive loop, consisting of pin 4 of MX003, R, Q, R, and pin 3 of the MX003, must be kept as short as possible and preferably routed over a ground plane. Relevant trace spacing (relating to trace creepage) must be observed according to applicable safety agency guidelines. 4

5 MX003-0W Evaluation Kit Figure 7. MX003 0W EV Kit Schematic S: DENOTES SECONDRY GROUND S S S U3 U U C NC R NC S D4 Q VDD C nf C8 47nF C9 47nF C0 C3 C C 470pF 3 T 9 8 T T 4T VDD VCC NDRV P CS MXTON FB V+ INDIV ES FREQ SS REF CON COMP VDD Q Z D3 MCT D M C C nf C 0.47µF C 0.47µF C4 0.47µF C 4.7nF 00V R 0.0Ω R3 0Ω R Ω R8 00Ω R4 0kΩ R 40kΩ R9 470Ω R kω R 0kΩ R4.4kΩ R3 80.kΩ R 39.kΩ R MΩ R 0kΩ L 4.7µH C4 0µF.3V C3 0µF.3V C7 0µF.3V VIN U MX003 T +VO -VO S -VIN

6 MX003-0W Evaluation Kit.0" Figure 8. MX003-0W EV Kit PC Board Layout Component Side.0" Figure 9. MX003-0W EV Kit Component Placement Guide Component Side. Note: Q and D4 are placed on the bottom side where their metal tabs are exposed to heatsink plate..0" Figure 0. MX003-0W EV Kit PC Board Layout Solder Side Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 0 San Gabriel Drive, Sunnyvale, C Maxim Integrated Products Printed US is a registered trademark of Maxim Integrated Products.